MKTEMP(1) NetBSD General Commands Manual MKTEMP(1)
NAMEmktemp -- make temporary file name (unique)
SYNOPSISmktemp [-dqu] [-ptmpdir] {-tprefix | template ...}
DESCRIPTION
The mktemp utility is provided to allow shell scripts to safely use tem-
porary files. It creates temporary files or directories using unique
names, and prints the names.
The name of each temporary file or directory is derived from a template
that includes several trailing `X' characters, such as /tmp/prefix.XXXX.
The trailing `X' characters in the template are replaced by unique values
derived from the current process number and additional letters or num-
bers. Any `X' characters other than at the end of the template are taken
literally. The number of unique file names mktemp can return depends on
the number of trailing `Xs' in the template; six `Xs' will result in
mktemp testing roughly 26 ** 6 combinations.
The templates used to create the unique names are derived from the -tprefix option, or the template arguments, possibly modified by other
options. Any number of temporary files or directories may be created in
a single invocation using multiple template arguments. It is possible to
specify both a -tprefix option and one or more template arguments, but
this is not usually done.
If neither a -tprefix option, nor any template arguments are specified,
then the default is equivalent to -t mktemp.
If mktemp can successfully generate a unique file name, the file is cre-
ated with mode 0600 (unless the -u flag is given) and the filename is
printed to standard output.
OPTIONS
The available options are as follows:
-d Make a directory instead of a file.
-ptmpdir
Specifies a directory in which temporary files should be created.
If this option is specified, then it applies to all temporary
files, including those created as a result of a -tprefix option,
and those created as a result of a template argument.
If the -ptmpdir option is not specified, then temporary files
created as a result of a -tprefix option will use a default tem-
porary directory (as described under the -t option), but tempo-
rary files created as a result of a template argument will not
use a default temporary directory (so they will be created rela-
tive to the current working directory, if the template does not
begin with `/').
-tprefix
Generate a template using an appropriate directory name, followed
by the supplied prefix, followed by `.XXXXXXXX'. Any `X' charac-
ters in the supplied prefix are taken literally, but the trailing
`X' characters in the appended `.XXXXXXXX' are replaced by unique
values.
The directory name used for the template generated by the -tprefix option is taken from the -ptmpdir option, or from the
TMPDIR environment variable, or /tmp as a default.
If one or more template arguments are used in addition to the -tprefix option, then the prefix does not apply to the template
arguments.
-q Fail silently if an error occurs. This is useful if a script
does not want error output to go to standard error.
-u Operate in ``unsafe'' mode. The temp file will be unlinked
before mktemp exits. This is slightly better than mktemp(3) but
still introduces a race condition. Use of this option is not
encouraged.
NOTESmktemp takes care to create the files or directories in a way that is
safe from race conditions (provided the -u option is not used).
Traditionally, without mktemp, many shell scripts created temporary files
using the name of the program with the pid as a suffix. This kind of
naming scheme is predictable and creates a race condition that allows an
attacker to subvert the program by creating a different file, directory,
or symbolic link under the same name. A safer, though still inferior,
approach is to make a temporary directory using the same naming scheme
While this does allow one to guarantee that a temporary file will not be
subverted, it still allows a simple denial of service attack. For these
reasons it is recommended that mktemp be used instead of simpler schemes.
Care should be taken to ensure that it is appropriate to use an environ-
ment variable potentially supplied by the user.
EXIT STATUS
The mktemp utility exits with a value of 0 on success, and 1 on any fail-
ure.
EXAMPLES
The following sh(1) fragment illustrates a simple use of mktemp where the
script should quit if it cannot get a safe temporary file.
TMPFILE=`mktemp /tmp/${0##*/}.XXXXXX` || exit 1
echo "program output" >> $TMPFILE
To allow the use of $TMPDIR:
TMPFILE=`mktemp -t ${0##*/}` || exit 1
echo "program output" >> $TMPFILE
In this case, we want the script to catch the error itself.
TMPFILE=`mktemp -q /tmp/${0##*/}.XXXXXX`
if [ $? -ne 0 ]; then
echo "$0: Can't create temp file, exiting..."
exit 1
fi
SEE ALSOmkdtemp(3), mkstemp(3), mktemp(3), environ(7)HISTORY
The mktemp utility appeared in NetBSD 1.5. It was imported from FreeBSD,
and the idea and the manual page were taken from OpenBSD.
NetBSD 7.0 November 4, 2012 NetBSD 7.0

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